The present invention relates to a method and system for determining with enhanced accuracy the direction or other location-related signal characteristics of a mobile radio transmitter, such as a cellular telephone, a personal digital assistant, a two-way pager, or other wireless communications device. Location-related services, such as 911 emergency system services, require timely and accurate information. One method for locating a mobile transmitter is to determine the transmitter""s directional bearings relative to two or more known locations, and to estimate the transmitter""s location based on where the lines of bearing intersect. Prior directional location approaches have been thwarted by the multifold directional ambiguities that are attendant to the use of standard communications antennas in the signal measurements process, and hence have employed augmentations to the conventional antennas. The present invention enables the straightforward usage of the conventional antenna configurations in extracting the location-related signal characteristics to support accurate location determination.
The present invention provides a system, apparatus, and method for measuring position-dependent characteristics of mobile radio signals from a mobile transmitter, including: receiving the transmitted signals at an antenna configuration having multiple phase-synchronized receiving elements, performing disambiguation processing for the extraction of position-dependent characteristics of the signals, and evaluating the characteristic parameters indicative of the transmitter""s position. The antenna configuration of the present invention may have three or more elements. These antenna elements may comprise at least one pair of elements whose inter-element separation is a large quantity of half wavelengths of the signals, and/or may comprise at least two pairs of elements whose inter-element separations differ by a small quantity of half wavelengths of the signals. The disambiguation processing may include the extraction of signal characteristics having reduced ambiguity for resolving the selection of the accurate positional interpretation of extracted ambiguous characteristics. Further, the disambiguation processing may include formation of differences of inter-element signal phase differences or of higher-order signal products. The evaluated characteristic parameters indicative of the transmitter""s position may include angle of arrival and/or may directly quantify the transmitter""s position.
In addressing the location-determination ambiguities mentioned above, a significant objective of the present invention is the innovative application of antenna configurations with elements structured and exploited to mitigate or avoid the highly ambiguous positional relations that can occur when standard communications antennas are used to sense signal characteristics indicative of transmitter positions. With such ambiguities thus addressed, a farther objective of the present invention is to enable the fall exploitation of the potential location-determination accuracy achievable through the use of such antenna configurations.